Marker device for rotationally orienting a stent delivery system prior to deploying a curved self-expanding stent

ABSTRACT

A stent for use in a curved body lumen is disclosed. The stent is made from a superelastic alloy such as nickel titanium or nitinol, and optionally includes a ternary element. The superelastic alloy has a low temperature phase or martensitic phase and a high temperature phase or an austenitic phase. In the high temperature phase, the stent has a curve along the length that closely matches the curve of the vessel in the patient&#39;s anatomy. When deployed in the curved vessel of the patient, the heat set curve of the stent closely conforms to the curvature in the vessel and minimizes trauma and stress to the vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pendingapplication having U.S. Ser. No. 09/586,211, filed Jun. 2, 2000,entitled “Curved Nitinol Stent For Extremely Tortuous Anatomy,” theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to self-expandingendoprosthetic devices. In particular, the present invention relates toself-expanding, intraluminal, vascular grafts, generally called stents,adapted to be implanted in a body lumen, such as carotid arteries,coronary arteries, peripheral arteries, veins, or other vessels tomaintain the patency of the lumen.

[0003] These devices are frequently used in the treatment ofatherosclerotic stenosis in blood vessels especially after percutaneoustransluminal angioplasty (PTA) or percutaneous transluminal coronaryangioplasty (PTCA) procedures, with the intent to reduce the likelihoodof restenosis of a vessel. Stents are also used to support a body lumen,tack-up a flap or dissection in a vessel, or in general where the lumenis weak to add support.

[0004] For example, during PTCA procedures, it is common to use adilation catheter to expand a diseased and partially occluded coronaryartery so that blood freely flows. Despite the beneficial aspects ofPTCA procedures and its widespread and accepted use, it has severaldrawbacks, including the possible development of restenosis and perhapsacute thrombosis and sub-acute closure. This recurrent stenosis has beenestimated to occur in seventeen to fifty percent of patients despite theinitial PTCA procedure being successful. Restenosis is a complex and notfully understood biological response to injury of a vessel which resultsin chronic hyperplasia of the neointima. This neonintimal hyperplasia isactivated by growth factors which are released in response to injury.Acute thrombosis is also a result of vascular injury and requiressystemic antithrombotic drugs and possibly thrombolytics as well. Thistherapy can increase bleeding complications at the catheter insertionsite and may result in a longer hospital stay. Sub-acute closure is aresult of thrombosis, elastic recoil, and/or vessel dissection.

[0005] Several procedures have been developed to combat restenosis andsub-acute or abrupt closure, one of which is the delivery andimplantation of an intravascular stent. Stents are widely usedthroughout the United States and in Europe and other countries.Generally speaking, the stents can take numerous forms, however, mostcommon is a generally cylindrical hollow tube that holds open thevascular wall at the area that has been dilated by a dilation catheter.One highly regarded stent used and sold in the United States is marketedunder the tradename ACS Multi-Link Stent, which is made by AdvancedCardiovascular Systems, Inc., Santa Clara, Calif.

[0006] For expandable stents that are delivered with expandablecatheters, such as balloon catheters, the stents are positioned over theballoon portion of the catheter and are expanded from a reduced deliverydiameter to an enlarged deployment diameter greater than or equal to theinner diameter of the arterial wall by inflating the balloon. Stents ofthis type are expanded to an enlarged diameter through deformation ofthe stent, which then engages the vessel wall. Eventual endothelialgrowth of the vessel wall covers over the stent.

[0007] Other stents are self-expanding where the expansion occursthrough the properties of the material constituting the stent. Examplesof intravascular stents can be found in U.S. Pat. No. 5,292,331 toBoneau; U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 4,856,516 toHillstead; U.S. Pat. No. 5,092,877 to Pinchuk; and U.S. Pat. No.5,514,154 to Lau et al.

[0008] One problem with some prior art stents, especially those of theexpandable type, is that they are often stiff and inflexible. Often, theexpandable type stents are formed from stainless steel alloys and areconstructed so that they are expanded beyond their elastic limit. Suchstents are permanently deformed beyond their elastic limits in order tohold open a body lumen and to maintain the patency of the body lumen. Bythe same token, since the material is stressed beyond its elastic limitinto the plastic region, the material becomes stiff and inflexible.

[0009] There are several commercially available stents that are widelyused and generally implanted in the coronary arteries after a PTCAprocedure. Another class of stents is implanted in vessels that arecloser to the surface of the body, such as in the carotid arteries inthe neck or in peripheral arteries and veins in the leg. Because thesestents are so close to the surface of the body, they are particularlyvulnerable to impact forces that can partially or completely collapsethe stent and thereby block fluid flow in the vessel. Since these priorart stents are plastically deformed, once collapsed or crushed, theyremain collapsed, permanently blocking the vessel. Thus, the prior artstents can pose an undesirable condition to the patient.

[0010] Other forces can impact the prior art stents and cause similarpartial or total vessel occlusion. Under certain conditions, musclecontractions might cause the prior art stents to partially or totallycollapse and to restrict blood flow in the vessel in which they areimplanted.

[0011] Such important applications as mentioned above have promptedstent designers to use superelastic or shape memory alloys in theirstent to exploit the materials'properties. An example of such shapememory alloy stents is disclosed in, for example, European PatentApplication Publication No. EP0873734A2, entitled “Shape Memory AlloyStent.” This publication suggests a stent for use in a lumen in a humanor animal body having a generally tubular body formed from a shapememory alloy which has been treated so that it exhibits enhanced elasticproperties.

[0012] The evolution of superelastic and shape memory alloy stentsprogressed to use of ternary elements in combination withnickel-titanium alloys to obtain specific material properties. Use of aternary element in a superelastic stent is shown in, for example, U.S.Pat. No. 5,907,893 to Zadno-Azizi et al. As a general proposition, therehave been attempts at adding a ternary element to nickel-titanium alloysas disclosed in, for instance, U.S. Pat. No. 5,885,381 to Mitose et al.

[0013] Another goal has been to design stents that are capable of easypassage through tortuous anatomies such as those found in a coronaryartery. One design entails a nitinol stent having a multiplicity ofundulating longitudinal struts that can readily change their lengths inthe longitudinal direction so as to provide increased longitudinalflexibility for the stent. An example of such a construction is shown inU.S. Pat. No. 5,879,370 to Fischell et al.

[0014] Designing stents for extremely curved and highly tortuousanatomies requires a stent that can bend sufficiently without the strutskinking. To address this kinking problem, one concept is to construct atubular stent with helically-arranged undulating members having aplurality of helical turns. Linking members formed by rings are laced orinterwoven between the undulations in adjacent turns of the helicalundulating members. U.S. Pat. No. 6,042,605 to Martin et al. disclosessuch a construction. The linked undulating elements facilitate bendingof the stent.

[0015] The foregoing stent designs address the problems with deliveringa straight length stent into a tortuous anatomy. These designs, do not,however, address the problems with deploying a straight length stent inan extremely curved vessel. Indeed, when a straight length stent isdeployed in a curved vessel, the stent tends to straighten the curvedvessel to follow the form of the stent. It is believed that thestraightening forces of the stent is damaging to the health of thevessel, may create emboli, and may generate intimal flaps that promoterestenosis.

[0016] One possible solution suggests assembling a composite stentpiecemeal at the curved vessel delivery site by using short modularsections. This approach is disclosed in U.S. Pat. No. 5,824,037 toFogarty et al. In this design, modular sections of the prosthesis may beselectively combined to form a composite prosthesis havingcharacteristics that are tailored to the specific requirements of thepatient. Each prosthetic module includes one or more standard interfaceends for engaging another module, the module interface typically havingends that overlap and/or lock within a predetermined axial range.Selection of the appropriate prosthetic modules and the flexibility ofthe interface overlap range provide a custom fit intraluminal prosthesistailored to the individual patient's needs. The module sections mayinclude bends, although the modules are individually introduced into alumen system of a patient's body so that the composite prosthesis isassembled in situ. Generally, the prosthetic body modules have a varietyof selectable body links, bends, and taper characteristics.

[0017] Although the foregoing conventional stent designs begin toaddress the problems with deploying a straight stent in an extremelytortuous or curved anatomy, there is, however, still a need for asuperelastic stent that is specifically intended for use in tortuousanatomies. The present invention satisfies this need.

SUMMARY OF THE INVENTION

[0018] The present invention is directed to a stent for use in a curvedbody lumen, comprising a cylindrically-shaped stent including asuperelastic alloy, wherein the stent has a unitary construction, andhas a length that is greater than a diameter. The superelastic alloy hasa low temperature phase that induces a first shape to the stent, and ahigh temperature phase that induces a second shape with a bend along thelength of the stent, and wherein the bend substantially conforms to thecurved body lumen.

[0019] In a preferred embodiment, the high temperature phase correspondsto an austenitic phase and the low temperature phase corresponds to amartensitic phase. Also, preferably, the superelastic alloy is anickel-titanium composite that may optionally include a ternary elementselected from the group of elements consisting of palladium, platinum,chromium, iron, cobalt, vanadium, manganese, boron, copper, aluminum,tungsten, tantalum, or zirconium.

[0020] In a preferred embodiment, a nickel-titanium or nitinolself-expanding stent can be heat set with various degrees of arch orcurvature along its length to accommodate a curved or tortuous vesselanatomy. Therefore, when the stent is deployed in a patient's body atabove the superelastic alloys phase transformation temperature, thestent reverts to its austenitic phase. In this state, the presentinvention stent assumes its expanded shape with a bend, wherein the bendwas heat set to match or approximate the curvature of the curved vessel.A taper may also be heat set into the stent so that it assumes a taperedand curved profile upon expansion.

[0021] Prior art self-expanding nitinol stents that have a straightlength, when deployed, exert a continuous radial force on the vesselwall at the deployment site. These prior art stents have a tendency tostraighten the lumen regardless of the lumen's natural curvature. Incontrast, the present invention stent with a heat set curve along itslength does not have the same tendency to straighten when inside thecurved vessel. Accordingly, trauma to the vessel is minimized and damageto the intima is diminished. Furthermore, the longitudinal bend or bendsthat are heat set into the present invention stent can vary in bothangle and radius of curvature. In various alternative embodiments, thepresent invention when in the high temperature state may include acurved length that bends in two dimensions, or may have a bend ofgreater than 90 degrees, or may have compound curves, or any combinationof the foregoing.

[0022] In the preferred embodiment, the present invention stent isunitary, being fashioned from a single piece of material. The presentinvention stent is also preferably of sufficient length to have anaspect ratio in which the length is greater than its diameter. Thisensures that the stent does not tip within the lumen, and minimizes thechance that the stent may migrate and cause an embolism.

[0023] The present invention may optionally include radiopaque markersthat assist the physician in proper orientation of the curved stent atthe deployment site. In particular, the radiopaque marker may includedirectional indicia that can be seen in a fluoroscope or by X-ray thathelp the physician recognize the orientation of the stent. Moreover, thepresent invention may be delivered by any delivery system and methodpresently known in the art.

[0024] The present invention further contemplates a delivery systemhaving a radiopaque pattern disposed on the delivery sheath wherein thepattern provides an indication to the physician as to the bend in theself-expanding stent when deployed inside the curved body lumen. Byusing the radiopaque marker as a point of reference, it is possible forthe physician to manipulate the delivery system and to deploy theself-expanding stent such that upon expansion of the self-expandingstent, the bend in the stent corresponds to the curvature in the lumen.

[0025] In a preferred embodiment, the radiopaque pattern includes atubular shape arrangement of rings interconnected by a spine. Thus, asthe stent delivery system is rotated within a curved anatomy, one radialalong the length of the stent delivery system exhibits constantradiopacity and the location exactly 180 degrees opposed has variableradiopacity as it is bent from concave to convex. When this location hasminimum radiopacity in a convex bend (and the spine assumes a concavebend), the stent delivery system is correctly oriented, and the curve ofthe self-expanding stent closely matches the curve of the anatomy.

[0026] Other features and advantages of the present invention willbecome more apparent from the following detailed description of theinvention when taken in conjunction with the accompanying exemplarydrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a partial cross-sectional view of a stent deliverysystem for use with the present invention.

[0028]FIG. 2 shows, in a cross-sectional view, the stent delivery systemof FIG. 1 with an optional expandable balloon.

[0029]FIG. 3 is a cross-sectional view of a curved vessel exposing adeployed stent of the present invention.

[0030]FIGS. 4a-4 f are schematic drawings of exemplary embodiments ofcurves and bends of the present invention stent; FIG. 4f specificallyillustrates a bend and a taper in the stent.

[0031]FIGS. 5a-5 b are cross-sectional views of an exemplary embodimentstent delivery system for use with the present invention showingdeployment of a curved self-expanding stent.

[0032]FIGS. 6a-6 c are a top plan view, a side elevational view, and anend view, respectively, of a preferred embodiment radiopaque pattern ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention in a preferred embodiment is directed to astent and delivery system for use in a curved body lumen. The stent ispreferably made of a superelastic alloy in which the material propertiesare exploited to achieve a specific curved shape for the stent whendeployed.

[0034] The stents of the present invention can have virtually anyconfiguration that is compatible with the body lumen in which they areimplanted. The radial force of the stent should be configured so thatthere is a substantial amount of open area once the stent has beendeployed. Preferably the open area to metal ratio is at least 400percent. The stent also should be configured so that dissections orflaps in the body lumen wall are covered and tacked up by the stent.

[0035] Referring to FIGS. 1, 2 and 3, in a preferred embodiment, a stent10 of the present invention is formed partially or completely of alloyssuch as nitinol (NiTi) which have superelastic (SE) characteristics. Thestent 10 is somewhat similar to the stent disclosed in, for example,U.S. Pat. No. 5,569,295, “Expandable Stents and Method for Making Same,”issued to Lam on Oct. 29,1996, which is incorporated herein by referencein its entirety.

[0036] The strut configuration of the stent 10 shown in FIG. 3 is justone example of many strut configurations that are contemplated by thepresent invention. In this embodiment, the stent 10 has a plurality ofradially expandable cylindrical elements 24 disposed generally coaxiallyto achieve a tubular form. This imaginary tube has a flexible butstraight length prior to deployment as shown in profile in FIGS. 1 and2.

[0037] In the deployed state in FIG. 3, the tubular form is curved alongits length to follow the curvature of the artery or vessel 28.

[0038] The radially expandable cylindrical elements 24 areinterconnected by spines 26 disposed between adjacent cylindricalelements 24 and that generally extend l the length of the stent 10. Theshape of the struts are designed so they can preferably be tightlypacked. This means that the serpentine shaped struts have extendedportions in one cylindrical element 24 that intrude into a complementaryspace within the circumference of an adjacent cylindrical element 24.

[0039] Furthermore, the stent 10 is unitary, meaning that it isfashioned from a single piece of material. For example, the stent 10 iscut to length from stock nitinol or like material tubing. The tubing isthen laser cut to form the strut pattern. Through this process, thepresent invention unitary stent construction avoids the processvariances and deficiencies of welded or mechanically linked togetherstents. Certainly engineering properties and dimensional tolerances canbe more easily controlled with a one-piece stent as compared to a stentpieced together from component parts.

[0040] As mentioned above, an exemplary stent of the present inventionincludes a superelastic material. The term “superelastic” refers toalloys having superelastic properties that include at least two phases:a martensitic phase, which has a relatively low tensile strength andwhich is stable at relatively low temperatures and an austenitic phase,which has a relatively high tensile strength and which is stable attemperatures higher than the martensitic phase. Superelasticcharacteristics generally allow the metal stent to be deformed bycollapsing and deforming the stent and creating stress which causes theNiTi to change to the martensitic phase. The stent is restrained in thedeformed condition within a delivery system to facilitate the insertioninto a patient's body, with such deformation causing the phasetransformation. Once within the body lumen, the restraint on the stentis removed, thereby reducing the stress therein so that the superelasticstent can return to its original undeformed shape by the transformationback to the austenitic phase.

[0041] More precisely, when stress is applied to a specimen of a metalsuch as nitinol exhibiting superelastic characteristics at a temperatureat or above that which the transformation of the martensitic phase tothe austenitic phase is complete, the specimen deforms elastically untilit reaches a particular stress level where the alloy then undergoes astress-induced phase transformation from the austenitic phase to themartensitic phase. As the phase transformation progresses, the alloyundergoes significant increases in strain with little or nocorresponding increases in stress. The strain increases while the stressremains essentially constant until the transformation of the austeniticphase to the martensitic phase is complete. Thereafter, further increasein stress is necessary to cause further deformation. The martensiticmetal first yields elastically upon the application of additional stressand then plastically with permanent residual deformation.

[0042] If the load on the specimen is removed before any permanentdeformation has occurred, the martensite specimen elastically recoversand transforms back to the austenitic phase. The reduction in stressfirst causes a decrease in strain. As stress reduction reaches the levelat which the martensitic phase transforms back into the austeniticphase, the stress level in the specimen remains essentially constant(but less than the constant stress level at which the austeniticcrystalline structure transforms to the martensitic crystallinestructure until the transformation back to the austenitic phase iscomplete); i.e., there is significant recovery in strain with onlynegligible corresponding stress reduction. After the transformation backto austenite is complete, further stress reduction results in elasticstrain reduction. This ability to incur significant strain at relativelyconstant stress upon the application of a load and to recover from thedeformation upon the removal of the load is commonly referred to assuperelasticity.

[0043] The prior art makes reference to the use of metal alloys havingsuperelastic characteristics in medical devices which are intended to beinserted or otherwise used within a patient's body. See, for example,U.S. Pat. No. 4,665,905 to Jervis and U.S. Pat. No. 4,925,445 toSakamoto et al.

[0044] Returning to FIG. 1, the graphic illustrates, in a partialcross-sectional view, a rapid exchange stent delivery system thatincludes a manipulating device 12, a guide wire 14, a delivery sheath16, and an intravascular catheter 18. The stent 10 is usually heldunderneath the delivery sheath 16, but FIG. 1 illustrates the systemwith the sheath 16 retracted. This simplified illustration of thedelivery system is just one example of many that may be used with thepresent invention. More details of a delivery system specifically foruse with a self-expanding stent may be found in, for example, U.S. Pat.No. 6,077,295, “Self-Expanding Stent Delivery System,” issued to Limonet al. on Jun. 20, 2000, which is incorporated herein by reference.Other delivery systems such as an over-the-wire delivery system may beused without departing from the scope of the instant invention.

[0045]FIG. 2 depicts in a partial cross-sectional view a variation ofthe delivery system of FIG. 1, which variation includes an optionalexpandable balloon 20 and an optional balloon inflation lumen 22. Thestent 10 is disposed over the expandable balloon 20, and the entireassembly is kept underneath the delivery sheath 16 until the moment thestent 10 is deployed. Again, this illustration shows the delivery sheath16 in the retracted condition.

[0046] The present invention stent 10 is preferably formed from asuperelastic material such as NiTi and undergoes an isothermaltransformation when stressed. The stent is first compressed to adelivery diameter, thereby creating stress in the NiTi alloy so that theNiTi is in a martensitic state having relatively low tensile strength.Alternatively, the present invention stent 10 may be chilled to its lowtemperature martensitic state and deformed into its small deliverydiameter. In either case, while still in the martensitic phase, thestent 10 is mounted onto a catheter by known methods such as adhesives,or other restraining means. By virtue of the superelastic properties,the stent 10 when mounted within the delivery sheath 16 tends to springback to a larger diameter, and pushes radially outward against theinside diameter of the sheath 16 when held therein.

[0047] In its delivery diameter, the overall diameter of the stent andcatheter are less than the inside diameter of an artery 28 or the vesselin which they are inserted. After the stent 10 is inserted into theartery or other vessel, the stress exerted by the stent 10 may bereleased by withdrawing the delivery sheath 16 in a proximal direction,whereupon the stent 10 immediately expands and returns to its original,undeformed shape by transforming back to the more stable austeniticphase. If the expandable balloon 20 of FIG. 2 is used, the stent 10 maybe further expanded by inflation of the expandable balloon 20 via theballoon inflation lumen 22 by known methods.

[0048] To exploit the properties of superelastic alloys, the presentinvention stent 10 can be heat set with various degrees of curvaturealong its length to conform to the curvatures of any number ofpatients'vasculatures. A conventional, superelastic stent that is heatset straight along its length, when deployed, exerts a continuous radialforce and attempts to straighten the lumen regardless of the lumen'soriginal anatomy or curvature. Therefore, in some cases, it may bebetter to deploy a self-expanding stent that more closely matches theoriginal curvature of the lumen to avoid these stresses upon the vessel.The arch shape that is heat set into the present invention superelasticstent 10 can vary in both total angle and radius of curvature.

[0049] For example, FIG. 3 is a partial cross-sectional view of a vessel28 having a particular curvature or bend 30. The superelastic stent 10has been deployed and is illustrated in its high temperature, expandedstate. In other words, the stent 10 is in its austenitic phase in whichthe stent 10 assumes a shape having a curvature or bend along its lengththat conforms and matches the curvature 30 of the vessel 28. Incontrast, prior to reaching the deployment site as depicted in FIG. 3,the stent 10 remains in its low temperature or martensitic state. Inthis state, the stent 10 is held inside the delivery sheath 16 and has ashape that does not include the bend shown in FIG. 3. In thismartensitic state, the present invention stent 10 is fairly pliable andfollows the flexures of the delivery system along the tortuous anatomyof the patient.

[0050] As seen in FIG. 3, the length of the stent 10 can be as long asneeded to perform its scaffolding function along the diseased portion ofthe vessel 28. In the exemplary embodiment, the diameter of stent 10 ispreferably smaller than the length of the stent 10 because this aspectratio ensures that the stent does not tip and migrate downstream causingan embolism. In its austenitic phase, the heat set curve along thelength of the stent 10 conforms closely to the natural bend 30 of thevessel 28. Ideally, this bend should follow the curvature 30 of thevessel 28 fairly closely. Therefore, the present invention contemplatesa variety of curvatures that may be heat set into the length of thesuperelastic stent 10 to match the unique vasculatures in differentpatients.

[0051]FIGS. 4a-4 f provide schematic views of the present inventionstent in its high temperature phase with a variety of induced bends andcurves along the length of the stent. More precisely, FIG. 4aillustrates a stent 32 having a 180 degree bend 34 along its length. InFIG. 4b, stent 36 has a 90 degree bend 38 along its length. FIGS. 4c and4 d illustrate stents 40 and 42 having multiple bends 44. FIG. 4eillustrates a stent 46 having a compound curve 48 in which the compoundcurve has at least two radii of curvature, r and R. FIG. 4f illustratesyet another alternative embodiment stent 50 having a bend 52 thatextends into three dimensions. In particular, the bend 52 occurs alongplane x-y, along plane x-z and along plane y-z. Any and all combinationsof the foregoing and other bends and curves known in the art are alsocontemplated.

[0052] The perspective view of FIG. 4f further illustrates a taper alongthe length of the stent 50. The tapered profile is created by having asmall diameter at the end of stent 50 facing out of the page and a largediameter at the end of stent 50 facing into the page. The taperedprofile is set into the stent 50 by applying the same processes as forimparting the bend 52, described elsewhere. Although the taperillustrated in FIG. 4f extends the entire length of the stent 50, it isunderstood that the taper may also assume a stepped configuration, orthe taper can be formed into just one end of the stent.

[0053] The delivery system for the present invention curved,self-expanding stent 10 can be as straight and as flexible as aconventional delivery system for a straight, self-expanding stent. Upondeployment, the superelastic stent assumes its heat set curved andexpanded shape shown in FIG. 3. The delivery system optionally includessome type of radiopaque marking to indicate the orientation of the stent10 prior to its deployment, thus allowing the physician to rotationallyposition the stent 10 such that its curvature or bend matches thecurvature or bend of the vessel. The delivery system at its proximalend, perhaps on the handle, may display markings to assist in physicianstent orientation and placement.

[0054] Optional radiopaque bands or markers 54 shown in FIGS. 1 and 2may be included on the stent 10 to assist the physician in orienting andpositioning the stent within the curved vessel 28. The radiopaquemarkers 54 may be in the form of bands as shown in FIGS. 1 and 2, theymay be coatings, they may be embedded within the stent, or they may besimply thicker or wider struts that appear more distinctly on afluoroscope. Also, selecting more radiopaque materials to alloy with thebase material is another solution. Preferably, the radiopaque markers 54have some unique directional indicia to assist the physician inrecognizing the orientation of the stent when viewed in atwo-dimensional screen such as a fluoroscope often found in a cath lab.

[0055] To illustrate, in an alternative embodiment shown in FIG. 4f,curved stent 50 has directional radiopaque markers 56 in the form ofchevrons that assist the physician in recognizing the orientation ofthis curved stent inside the patient's vasculature. Although as shown inFIG. 4f the stent 50 is in its expanded, deployed state, the chevronmarkers 56 nevertheless are effective in the compressed deliverydiameter to help with placement and orientation.

[0056] The present invention superelastic alloy is preferably formedfrom a nickel-titanium composition known in the art. The process to heatset the curved shape of the present invention stent is performed bymounting the stent on a mandrel having the desired curvature, taper,etc., and raising the temperature of the stent to a point above theaustenitic finish (A_(f)) of the material. The process details for heatsetting a nickel-titanium alloy is well known in the art. After the heatset procedure, the stent 10 is removed from the mandrel and returned toroom temperature. In the exemplary embodiment, the nitinol alloy has atransition temperature that is below human body temperature, andpreferably below room temperature.

[0057] The superelastic alloy of the present invention may alternativelybe formed from a composition consisting essentially of about 30 to about52 percent titanium and the balance nickel and up to 10 percent of oneor more additional ternary alloying elements. Such ternary alloyingelements may be selected from the group consisting of palladium,platinum, chromium, iron, cobalt, vanadium, manganese, boron, copper,aluminum, tungsten, tantalum, or zirconium. In particular, the ternaryelement may optionally be up to 10 percent each of iron, cobalt,platinum, palladium, or chromium, and up to about 10 percent copper andvanadium. As used herein, all references to percent composition areatomic percent unless otherwise noted.

[0058] In another preferred embodiment, a NiTi stent with SME (shapememory effect) is heat-treated at approximately 500 degrees C. The stentis mechanically deformed into a first, smaller diameter for mounting ona catheter delivery system, such as the delivery system of FIG. 2, thatincludes the expandable balloon 20 and the balloon inflation lumen 22.After the stent has been expanded by the balloon and deployed againstarterial wall 29 of artery 28, 45 degrees C. heat is applied causing thestent to return to its fully expanded, curved length and to contact thecurved arterial wall of the artery. The application of 45 degrees C. ofheat is compatible with most applications in the human body, but it isnot to be limited to this temperature as higher or lower temperaturesare contemplated without departing from the invention. The 45 degrees C.temperature can be achieved in a conventional manner well known in theart such as by warm saline injected into the delivery catheter andballoon.

[0059] The shape memory characteristics allow the devices to be deformedto facilitate their insertion into a body lumen or cavity and then to beheated within the body so that the device returns to its original,curved-length shape. Again, alloys having shape memory characterisitcsgenerally have at least two phases: a martensitic phase, which has arelatively low tensile strength and which is stable at relatively lowtemperatures, and an austenitic phase, which has a relatively hightensile strength and which is stable at temperatures higher than themartensitic phase.

[0060] Shape memory characteristics are imparted to the alloy by heatingthe metal to a temperature above which the transformation from themartensitic phase to the austenitic phase is complete; i.e., atemperature above which the austenitic phase is stable (A_(f)). Thecurved shape of the metal during this heat treatment is the curved shape“remembered.” The heat-treated metal is cooled to a temperature at whichthe martensitic phase is stable, causing the austenitic phase totransform to the martensitic phase. The metal in the martensitic phaseis then plastically deformed, e.g., to facilitate the entry thereof intoa patient's body via a delivery system. Subsequent heating of thedeformed martensitic phase to a temperature above the martensite toaustenite transformation temperature causes the deformed martensiticphase to transform to the austenitic phase. During this phasetransformation the metal reverts back to its original curved shape.

[0061] The recovery or transition temperature may be altered by makingminor variations in the composition of the metal and in processing thematerial. In developing the correct composition, biological temperaturecompatibility must be determined in order to select the correcttransition temperature. In other words, when the stent is heated, itmust not be so hot that it is incompatible with the surrounding bodytissue. Other shape memory materials may also be utilized, such as, butnot limited to, irradiated memory polymers such as autocrosslinkablehigh density polyethylene (HDPEX). Shape memory alloys are known in theart and are discussed in, for example, “Shape Memory Alloys,” ScientificAmerican, Vol. 281, pp. 74-82 (Nov. 1979).

[0062] Shape memory alloys undergo a transition between an austeniticstate and a martensitic state at certain temperatures. When they aredeformed while in the martensitic state they retain this deformation aslong as they are retained in this state, but revert to their originalconfiguration when they are heated to a transition temperature, at whichtime they transform to their austenitic state. The temperatures . atwhich these transitions occur are affected by the nature of the alloyand the condition of the material. Nickel-titanium-based alloys (NiTi),wherein the transition temperature is slightly lower than bodytemperature, are preferred for this embodiment of the present invention.It is desirable to have the transition temperature set at just belowbody temperature to enable a rapid transition from the martensitic stateto the austenitic state when the stent is implanted in a body lumen.

[0063] Turning again to FIGS. 2 and 3, the stent 10 is formed from ashape memory alloy, such as NiTi discussed above. When positioned at thedelivery site within the vessel, the protective sheath 16 is retractedto expose the stent 10. The stent 10 then immediately expands due tocontact with the higher temperature within artery 28 as described abovefor devices made from shape memory alloys. The stent 10 assumes itscurved shape in the austenitic state and its curved shape closelyconforms to the curvature 30 of the artery 28. After the stent 10 isdeployed at the curved artery 28, the expandable balloon 20 is inflatedvia the balloon inflation lumen 22 by conventional means so that thestent 10 expands radially outward. The balloon 20 may optionally becurved (not shown) when inflated to follow the natural curvature 30 ofthe artery 28. The bend in the inflated balloon also avoidsstraightening out the curved, expanded stent.

[0064]FIGS. 5a and 5 b are cross-sectional views of a preferredembodiment of the present invention stent and delivery system.Specifically, FIGS. 5a and 5 b show the devices in a state prior todeployment of the curved stent in the curved lumen, and post deploymentof the curved stent in the lumen, respectively. In the exemplaryembodiment shown, an over-the-wire catheter 62 has a guide wire lumen 64that extends through the catheter 62 and receives a guide wire 68therein. Generally speaking, in order to implant a self-expanding stent70, the guide wire 68 is advanced through a patient's body lumen to astenosed region 72. Typically, the guide wire 68 extends past thestenosed region 72. Next, a distal end 74 of the over-the-wire catheter62 is threaded over the proximal end of the guide wire that is outsidethe patient (not shown) and the catheter 62 is advanced along the guidewire 68 until the distal end 74 of the catheter 62 is positioned withinthe stenosed region 72.

[0065] An outer member 76, sometimes referred to as a delivery sheath,is elastic and maintains a compressive force over the self-expandingstent 70. As a result, the compressed self-expanding stent maintains asmall profile during delivery to the stenosed region 72.

[0066] As depicted in FIG. 5b, the self-expanding stent 70 is deployedin the stenosed region 72 by moving the outer member 76 in a proximaldirection while simultaneously moving an inner member 78 in a distaldirection. Optionally, the inner member 78 can be maintained stationarywhile the outer member 76 is moved in the distal direction to expose theself-expanding stent 70 thereby deploying the stent 70 at the stenosedregion 72.

[0067] The stent 70 cannot slide or move axially on the outer surface80, because the open lattice structure of the stent 70 engages a matrixof surface contours 82. As portions of the self-expanding stent 70 areno longer contained by the outer member 76, those portions expandradially outward into contact with the vessel wall 60 in the area of thestenosed region 72. When fully deployed and implanted, as shown in FIG.5b, the stent 70 supports and holds open the stenosed region 72 so thatblood flow is not restricted. The surface contours 82 do not inhibit thestent 70 from self-expanding radially outward; they only impede axialmovement of the stent 70, which improves the precision of the appositionof the stent relative to the stenosed region 72.

[0068] With certain self-expanding stents, there is a tendency of thestent to shorten somewhat when it expands. When the stent shorteningoccurs, the physician may find that the stent has been improperly placedin the stenosed region if the effects of the shortening have not beentaken into consideration. Accordingly, it may be necessary to move theinner member 78 distally in order to compensate for the stent shorteningupon expansion of the stent. It is also possible due to stent designthat the self-expanding stent does not appreciably shorten uponexpansion. If this is the case, it is then unnecessary to move the innermember 78 distally while simultaneously moving the outer member 76proximally in order to release the self-expanding stent 70 in the bodylumen. With a stent configuration that does not appreciably shortenduring expansion, the outer member 76 is moved proximally while theinner member 78 remains stationary as the self-expanding stent 70expands radially outwardly into contact with the vessel wall 60. Afterthe stent 70 is implanted and contacts the stenosed region 72, theover-the-wire catheter 62 is withdrawn from the patient's vasculature,completing the procedure.

[0069] The relative movement between the inner member 78 and the outermember 76 is accomplished by manipulation of the control handles 84, 86.The control handles 84, 86 can take the form of a thumb-switch, arotating-screw, or a ratcheting arrangement, or the like. Such controlhandle mechanisms are well known in the art. The control handles 82,84are located at the proximal end 88 of the catheter 62 for convenientaccess and manipulation by the physician. The foregoing delivery systemis further described in detail in U.S. Pat. No. 6,077,295 to Limon etal., whose entire contents are hereby incorporated by reference.

[0070] As shown in FIGS. 5a and 5 b, the vessel wall 60 has a bend 90.It is therefore important that the bend in the self-expanding stent 70closely follows the vessel bend 90 upon deployment of the stent.Otherwise, the bias in the expanded stent 70 with its bend improperlyaligned with the bend 90 in the vessel may impart trauma to the stenosedregion 72 due to the misfit. It is thus useful for the physician to knowbeforehand the location and direction of the bend in the stent 70 priorto deployment such that the stent bend can be matched to the bend 90 inthe vessel wall 60.

[0071] Still in the drawings, FIGS. 5a and 5 b show the distal end 74 ofthe catheter 62 optionally embedded with a radiopaque marker pattern 92.This exemplary embodiment radiopaque marker pattern 92 is illustrated ina top plan view, side elevational view, and end view in FIGS. 6a, 6 b,and 6 c, respectively. The radiopaque marker pattern 92 has a spine 94interconnecting a plurality of rings 96 that are aligned coaxially togenerally form a tubular shape. The cross-sectional area of the rings 96may be a rectangle as shown in the figures or can be any other of avariety of shapes. Likewise, the cross-sectional shape of the spine 94is shown to be a circular shape, but other shapes are contemplated.

[0072] The illustrations of FIGS. 6a-6 c depict the radiopaque markerpattern 92 in its undistorted condition, while the radiopaque markerpattern 92 is shown in FIGS. 5a and 5 b in first a bent condition andthen in a straight condition, respectively. The bent state of theradiopaque marker pattern 92 in FIG. 5a occurs when the spine 94 isrotationally and axially aligned with the bend 90 in the curved vesselwall 60. The bent state of the radiopaque marker pattern 92 isdiscernible by a physician using a fluoroscope or similar viewingdevice.

[0073] The spine 94 presents more radiopaque mass and generates astronger image on the fluoroscope than the spaced apart rings 96.Therefore, if the heat set bend in the self-expanding stent 70 isoriented relative to the location of the spine 94 when contained insidethe outer member 76, the physician is insured that when deployed, thebend in the stent 70 will closely match the bend 90 in the vessel wall60. If the alignment is not acceptable, the physician can torque thecatheter 62 prior to deployment until the image of the radiopaque markerpattern 92 and specifically the spine 94 is aligned with the curvatureof the bend 90. Axial adjustments are also possible to align the distaland proximal ends of the stent with the stenosed region 72. When therotational and axial alignments are achieved, the stent 70 can bedeployed from the catheter 62.

[0074]FIG. 6a-6 c are various views of a preferred embodiment radiopaquemarker pattern 92. In this embodiment, the rings 96 are evenly spacedapart, but asymmetrically located along the length of the spine 94 suchthat one of the spine extends farther from the end than the other. Thisasymmetrical pattern is helpful in recognizing the proximal versusdistal ends of the stent when viewed in a fluoroscope, for example. Thephysician can then discern the direction the stent is facing. Thedirection the stent is facing is sometimes critical because the stentmight include a taper and the physician would need to recognize whetherthe taper when deployed pointed distally or proximally.

[0075] The radiopaque marker pattern 92 shown in FIGS. 6a-6 c can be, invarious exemplary embodiments, constructed by laser cutting a tube ofradiopaque material such as gold, platinum, tantalum, tungsten, barium,bismuth, or like materials. The identical pattern can be cut into thesurface of the outer member 76 by use of plasma or laser etch, grindererosion, or acid etch. The radiopaque marker pattern 92 is then embeddedinto the etched surface of the outer member 76 proximate to the distalend 74.

[0076] The radiopaque marker pattern 92 can be affixed to the etchedsurface of the outer member 76 by use of a glue. Alternatively, heatshrinking then cooling of the polymer material used for the outer member76 expands the material to create a tight fit with the radiopaque markerpattern 92. Other methods known in the art can of course be used toattach the radiopaque marker pattern 92 to the outer member 76.

[0077] In the exemplary embodiment of the present invention depicted inFIGS. 5a, 5 b, the inner member 78 and outer member 76 can be formedfrom polymeric materials such as latex, silicone, C-Flex, Tecoflex,polyurethane, polyethylene terephthalate (PET), polyethylene ethylketone (PEEK), polytetrafluorethylene (PTFE), nylon elastomer (PEBAX),and other materials known in the art. The surface contours 82 can bemade in a preferred embodiment from polyurethane, elastomericpolyesters, and the like. In an alternative embodiment, the radiopaquemarker pattern 92 can be formed from a polymeric material such as apolyether block amide (e.g. PEBAX) loaded with from approximately 60percent to 90 percent of tungsten particles. The polymeric radiopaquemarker pattern 92 can then be thermally bonded to the outer member 76.Because the outer member 76 and the radiopaque marker pattern 92 areboth made of a polymeric material, both can expand or contract together.Other polymers used for markers as well as various radiopaque filleragents known in the art can be used together instead of the PEBAXmaterial.

[0078] It is also possible in another alternative embodiment to providethe tubular structure of the radiopaque marker pattern 92 made of aradiopaque metal, and to shrink wrap the polymer outer member 76 overthe radiopaque marker pattern 92. This process is known in the art. Inyet another process, the polymeric outer member 76 is swaged or neckeddown to a thinner wall thickness so that the radiopaque marker pattern92 can be glued thereon. Once released, the polymeric material returnsto its original condition through elasticity and the marker pattern 92is embedded therein. Once embedded, the radiopaque marker pattern 92sits flush with the surface of the outer member 76. Optional grooves canbe etched into the surface of the outer member 76 for even betterseating as described earlier.

[0079] Installation of the curved stent 70 into the catheter 62 shouldpreferably be coordinated with the orientation of the radiopaque markerpattern 92 in the outer member 76. In one exemplary embodiment, the bendin the self-expanding stent 70 should be rotationally aligned with thespine 94 of the radiopaque marker pattern 92 such that deployment of theself-expanding stent 70 causes the bend in the stent 70 to coincide withthe location of the spine 94. Thus, if the physician aligns the spine 94with the curved vessel wall 60, the physician is insured that thedeployed stent 70 has a bend that matches the natural curve of thevessel wall 60. This orientation of the spine 94 in the radiopaquemarker pattern 92 is illustrated in FIG. 5a wherein the spine 94 assumesa convex shape and the diametrically opposed side assumes a concaveshape. Deployment of the stent 70 at this juncture promotes a good matchbetween the bend in the stent 70 and the bend 90 in the vessel wall 60,as shown in FIG. 5b.

[0080] Alternatively, the spine 94 can be rotated 180 degrees out ofphase from the orientation shown in FIG. 5a, insofar as the physician isfirst informed of how the self-expanding stent 70 will expand and theattitude of the bend in the stent upon deployment. In this alternativeorientation, the spine 92 assumes a concave shape and the diametricallyopposed side assumes a convex shape (not shown). When properly aligned,the bend in the stent 70 matches the bend 90 of the curved vessel wall60.

[0081] Accordingly, the present invention stent delivery system containsa radiopaque marker that has one radiographic image along the insideradius of curvature when properly bent and a second radiographic imagealong the outside radius of curvature when properly bent. When theseimages are oriented correctly relative to the vascular anatomy, theself-expanding stent can be deployed. Thus, it is preferable to have aspine 24 to create sufficient radiopaque mass that is apparent on thefluoroscope and to omit this mass at 180 degrees out of phase from thespine, as seen in FIG. 6b. As the stent delivery system is rotatedwithin the curved anatomy, one radial location along the length of thestent delivery system exhibits constant radiopacity; the locationexactly 180 degrees opposed exhibits variable radiopacity as it is bentfrom concave to convex. When this location has minimum radiopacity, thestent delivery system is correctly oriented and the curve of theself-expanding stent agrees with the curve of the anatomy.

[0082] Of course, as shown in FIGS. 5a and 5 b, the radiopaque markerpattern can be used 180 degrees out of phase from the orientation justdescribed so that the convex portion of the curve is aligned with thespine 94 and the concave portion of the bend is aligned with an area 180degrees out of phase with the spine 94. In such case, two solidradiopaque images appearing on the fluoroscope indicate that the bentstent is properly positioned in the curved anatomy and is ready fordeployment.

[0083] Hence, one approach is to locate a large, radiopaque mass alongthe length of the radiopaque marker pattern 92 and to locate a small,radiopaque mass at 180 degrees out of phase from the large radiopaquemass. Following this objective, many alternative embodiment radiopaquemarker patterns are contemplated aside from that shown in FIGS. 6a-6 c.

[0084] While the present invention has been illustrated and describedherein in terms of a superelastic stent and delivery system wherein thestent assumes a curved shape in its high temperature state, it isapparent to those skilled in the art that the present invention can beused in other instances. Other modifications and improvements may bemade without departing from the scope of the present invention.

What is claimed is:
 1. A self-expanding stent and delivery system fordeploying the self-expanding stent in a curved body lumen, comprising: acylindrically-shaped self-expanding stent including a superelasticalloy, wherein the superelastic alloy includes a low temperature phasethat induces a first shape to the stent, and a high temperature phasethat induces a second shape with a bend along a length of the stent,wherein the bend substantially conforms to the curved body lumen; adelivery sheath having a hollow interior at least partially containingthe stent in the first shape; a radiopaque pattern disposed in thedelivery sheath, wherein the pattern includes a tubular shapearrangement of rings interconnected by a spine; wherein the stent ispositioned in the delivery sheath so that the bend in the stent isoriented relative to the spine.
 2. The self-expanding stent and deliverysystem of claim 1 , wherein the radiopaque pattern includes a radiopaquematerial selected from the group consisting of gold, platinum, tantalum,tungsten, barium, or bismuth.
 3. The self-expanding stent and deliverysystem of claim 1 , wherein the high temperature corresponds to anaustenitic phase and the low temperature corresponds to a martensiticphase.
 4. The self-expanding stent and delivery system of claim 1 ,wherein the spine includes a circular cross-sectional shape.
 5. Theself-expanding stent and delivery system of claim 1 , wherein thesuperelastic alloy includes nickel and titanium.
 6. The self-expandingstent and delivery system of claim 1 , wherein the second shape includesa tapered profile.
 7. The self-expanding stent and delivery system ofclaim 1 , wherein the superelastic alloy includes a nickel-titaniumalloy with at least 30 to 52 percent titanium, and a ternary elementthat is selected from the group of elements consisting of palladium,platinum, chromium, iron, cobalt, vanadium, manganese, boron, copper,aluminum, tungsten, tantalum, or zirconium.
 8. The self-expanding stentand delivery system of claim 7 , wherein the superelastic alloy includesat least 38 percent nickel and up to 10 percent of the ternary element.9. The self-expanding stent and delivery system of claim 1 , wherein theradiopaque pattern is embedded to the delivery sheath.
 10. Aself-expanding stent and delivery system for deploying theself-expanding stent in a curved body lumen, comprising: acylindrically-shaped self-expanding stent including a superelasticalloy, wherein the superelastic alloy includes a low temperature phasethat induces a first shape to the stent, and a high temperature phasethat induces a second shape with at least one bend along a length of thestent, wherein the at least one bend substantially conforms to at leasta curved section of the curved body lumen; an elastic delivery sheathhaving a hollow interior at least partially restraining the stent in thefirst shape; a flexible radiopaque pattern disposed in the deliverysheath, wherein the pattern includes a tubular shape arrangement ofrings interconnected by a spine; wherein the stent is held in thedelivery sheath so that the bend in the stent is oriented relative tothe spine.
 11. The self-expanding stent and delivery system of claim 10, wherein the bend in the stent is aligned proximate to the spine whenthe stent is held inside the delivery sheath.
 12. The self-expandingstent and delivery system of claim 10 , wherein the bend in the stent isoriented approximately 180 degrees rotation from the spine when thestent is held inside the delivery sheath.
 13. The self-expanding stentand delivery system of claim 10 , wherein the second shape includes ataper along a length thereof.
 14. The self-expanding stent and deliverysystem of claim 10 , wherein the superelastic alloy includesnickel-titanium alloy having an austenitic phase above approximately 37degrees C.
 15. The self-expanding stent and delivery system of claim 10, wherein the delivery sheath includes a polymer and the radiopaquepattern is embedded in the polymer.
 16. A process for deploying aself-expanding stent in a curved body lumen with a delivery system,comprising: providing a cylindrically-shaped self-expanding stentincluding a superelastic alloy, wherein the superelastic alloy includesa low temperature phase that induces a first shape to the stent, and ahigh temperature phase that induces a second shape with a bend along alength of the stent, wherein the bend substantially conforms to thecurved body lumen; providing a delivery sheath having a hollow interiorat least partially containing the stent in the first shape; providing aradiopaque pattern in the delivery sheath, wherein the pattern includesa tubular shape arrangement of rings interconnected by a spine;installing the stent in the first shape inside the delivery sheath;positioning the stent in the delivery sheath so that the bend in thestent is oriented relative to the location of the spine.
 17. The processfor deploying a self-expanding stent in a curved body lumen of claim 16, wherein the process includes orienting the bend in the stent inapproximate alignment with the spine.
 18. The process for deploying aself-expanding stent in a curved body lumen of claim 16 , wherein theprocess includes orienting the bend in the stent approximately 180rotational degrees from the spine.
 19. The process for deploying aself-expanding stent in a curved body lumen of claim 16 , wherein thesuperelastic alloy includes a nickel-titanium alloy having a lowtemperature martensitic phase and a high temperature austenitic phase.20. The process for deploying a self-expanding stent in a curved bodylumen of claim 16 , wherein the radiopaque strut pattern is fabricatedfrom wire.